The present invention relates to a golf ball capable of enhancing the resilience to increase the carry of the ball, realizing player""s soft feeling of hitting the ball, and improving the durability against cracking.
A method of improving a cover material by adding an inorganic filler (titanium dioxide and barium sulfate) thereto has been proposed, for example, in Japanese Patent Laid-open No. Hei 6-277312. The addition of titanium dioxide and barium sulfate to the cover of a golf ball is effective to give excellent properties such as a carrying performance to the golf ball. With respect to the reason for this, the document describes that the addition of titanium dioxide and barium sulfate to the cover xe2x80x9cshifts a weight distribution in the ball from the core center to the cover side, to increase an inertia moment of the ball, thereby increasing the carry of the golf ballxe2x80x9d.
Such a proposal, however, has been required to be further improved in terms of factors determining golf ball performances, for example, a hardness factor of the cover and core, a composition factor of the cover and core, and a dimple factor. In particular, the ball disclosed in the embodiment of the above proposal has been required to be improved in terms of feeling of hitting the ball and the carry of the ball.
On the other hand, Japanese Patent Laid-open No. Hei 9-215778 has proposed a two-piece solid golf ball improved in its carry, controllability, and linearity by using a cover material having a relatively large specific gravity and optimizing the cover hardness, inertia moment, and dimple pattern.
The solid golf ball of the above document, however, has the following problem: namely, in the case of using a thermoplastic urethane elastomer or the like as the cover material, if the cover hardness is set in a softer range (near Shore hardness 50), the golf ball exhibits high performances; however, if the cover hardness is set in a harder range (near Shore hardness 60), it may often fail to simultaneously improve the resilience, durability against cracking, and player""s soft feeling of hitting the ball.
The golf ball of the above document has been also required to be optimized in terms of the inertia moment.
On the other hand, the properties of a golf ball strongly demanded by golf players are generally player""s soft feeling at the time of hitting the ball and the carrying performance of the ball; however, it is regarded as difficult to make both the properties compatible with each other for the following reasons:
(1) If the core is softened for ensuring the player""s soft feeling, a deformed amount of the hit ball becomes large, to degrade the durability against cracking.
(2) If both the core and cover are softened for ensuring both the player""s soft feeling and durability against cracking, the resilience and initial velocity of the ball are reduced, to sacrifice the carrying performance.
(3) If the ball is excessively improved only in terms of the player""s soft feeling, the other properties are sacrificed, to cause such an inconvenience that local deformation of the hit ball becomes large, not to keep the sphericalness of the ball at the initial stage of the carry of the ball, thereby degrading the carrying performance.
To solve the above problems, Japanese Patent Laid-open No. 2000-5341 has proposed an excellent golf ball characterized by combining a core, which is softened to improve the player""s soft feeling and durability against cracking, with a cover to which a reinforcement filler is added.
Such a golf ball, however, has been required to be further improved in terms of resilience, carry, player""s soft feeling of hitting the ball, and durability against cracking.
An object of the present invention is to provide a golf ball capable of enhancing the resilience to increase the carry of the ball, realizing player""s soft feeling of hitting the ball, and improving the durability against cracking.
As a result of an examination made by the present inventor in order to achieve the above object, it has been found that a golf ball including: a core and a cover made from a cover material mainly containing an ionomer resin and also an inorganic filler having a specific gravity of 3.50 or more in an amount of 10 to 25 parts by mass on the basis of 100 parts by mass of the ionomer resin; wherein a flexural amount of the core, measured by applying a load of 980 N thereto, is in a range of 4.7 to 5.3 mm; a specific gravity of the cover material is in a range of 1.050 to 1.100, a thickness of the cover is in a range of 1.5 to 2.0 mm, and a Shore D hardness of the cover is in a range of 57 to 63; a weight of the golf ball is in a range of 45.0 to 46.0 g, and a flexural amount of the golf ball, measured by applying a load of 980 N thereto, is in a range of 3.7 to 4.3 mm; and a weight (W) of the golf ball and an inertia moment (MI) thereof satisfy a relationship of 1.53xc3x97W+13.32xe2x89xa6MIxe2x89xa61.61xc3x97W+11.02, is advantageous in enhancing the resilience to increase the carry of the ball, realizing player""s soft feeling of hitting the ball, and improving the durability against cracking by a synergism effect of the above-described optimized requirements. The reasons for this are as follows:
(1) Since each of the core and ball is very softened by optimizing the flexural amount thereof, it is possible to lower the spin of the ball and hence to improve the carry of the ball, and also to realize player""s soft feeling.
(2) Since the hardness of the cover is set to a suitable value (near Shore D hardness 60), it is possible to keep high resilience while keeping good player""s feeling of hitting the ball.
(3) Since an inorganic filler having a particular specific gravity is added to the cover, it is possible to suppress degradation of the durability against cracking due to realization of player""s soft feeling of hitting the ball, and since the mixing ratio of the inorganic filler is optimized, it is possible to suppress a reduction in initial velocity of the hit ball due to excessive addition of the inorganic filler to the cover resin.
(4) Since an inertia moment suitable to a low spin structure (relatively harder cover+soft core) is realized, it is possible to increase the carry of the ball.
(5) Since the core is made from a rubber composition including an organic sulfur compound as needed and also the kind of the ionomer resin is specified as needed, it is possible to further improve the resilience, and since the dimples are optimized, it is possible to further improve the carrying performance.
Accordingly, the present invention provides a golf ball including: a core and a cover made from a cover material mainly containing an ionomer resin and also an inorganic filler having a specific gravity of 3.50 or more in an amount of 10 to 25 parts by mass on the basis of 100 parts by mass of the ionomer resin; wherein a flexural amount of the core, measured by applying a load of 980 N thereto, is in a range of 4.7 to 5.3 mm; a specific gravity of the cover material is in a range of 1.050 to 1.100, a thickness of the cover is in a range of 1.5 to 2.0 mm, and a Shore D hardness of the cover is in a range of 57 to 63; a weight of the golf ball is in a range of 45.0 to 46.0 g, and a flexural amount of the golf ball, measured by applying a load of 980 N thereto, is in a range of 3.7 to 4.3 mm; and a weight (W) of the golf ball and an inertia moment (MI) thereof satisfy a relationship of 1.53xc3x97W+13.32xe2x89xa6MIxe2x89xa61.61xc3x97W+11.02.
In the above golf ball, the inorganic filler preferably contains barium sulfate and titanium dioxide.
The ionomer resin is preferably composed of an Li ion neutralized ionomer resin and a Mg ion neutralized ionomer resin.
The core is preferably made from a rubber composition containing polybutadiene as a main rubber component and also an organic sulfur compound.
A diameter of the golf ball is preferably in a range of 42.65 to 42.75 mm
The golf ball preferably has in the cover surface a large number of dimples; and a dimple total volume ratio (VR) is preferably in a range of 0.85% or less, the dimple total volume ratio being defined as a ratio of a total volume of dimple spaces each of which is present under a plane surface surrounded by an edge portion of the dimple to a total volume of a virtual ball being the same as the golf ball except that the virtual ball has no dimples.
The Shore D hardness of the cover is preferably set to 60.
The thickness of the cover is preferably set to 1.9 mm.
The specific gravity of the cover is preferably set to 1.090.
A flexural amount of the core, measured by applying a load of 980 N thereto, is preferably set to 5.0 mm.
The flexural amount of the golf ball, measured by applying a load of 980 N thereto, is preferably set to 4.0 mm.